A qustion about samba

[M.Saeed Ansari]

Hello ,
I'm a student in Shahed university in IRAN .
Now I'm become a member of our uni IT-Center .
We are going to have an organized network with a en-bloc user
authentication and proxy server.
In comparison between MS AD and Samba ,  i want to choose Samba server
( cause of my belief in Open Source ) .
Our plan have a Forest(root : shahed.ac.ir) and trees for faculties
(like : eng.shahed.ac.ir  , maybe have child ) and maybe for
internet-site we may have a new forest (we should have trust between
these domains ).
In every site we should have DC and SQUID Proxy server ( for control
and sharing internet in the best way ) .
note : all of our clients have windows XP or se7en .
My questions are :
can we completely handle our plan with Samba server ? , for
replication and trust what we should do ?  we should use openLDAP for
our plan ? what is your suggestion for what we are going to do ? witch
distribution of LINUX is appropriate for our plan ?

Best regards .
-- 
M.S.Ansari